My astronomy project:
TS130 refractor to Nikon D800 adapter

Content:

1. TS130 to Nikon adapter
2. Adapter prototype
3. Implement of a duo narrow filter
4. Preparing for first light
5. Aberration analyze
6. Shorten the adapter length
7. Adjust tilt and back focus
8. New bracket for guide camera
9. Baffles
10. Prism bracket
11. RayTrace advanced
12. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information on your own risk!

9: Baffles

When I started to take astrophotos with this new setup I noticed that there where some static pattern in the images. Concentric circles and they wasn't there in the old setup. First I thought that it was the flat calibration that went wrong, but even without flats they are there. Examining the construction, it's not very different from earlier, the camera is changed from Canon 6D to Nikon D800, both full frame cameras. A new shorter adapter between the field flatter and camera. Not much that could go wrong.

After some thought and some tests, I think it's light leaking in from unwanted reflections.

First baffle:

If I place a baffle into the adapter I can block the stray light that leaking into the camera sensor.

I designed a baffle that I can put in and easy to remove. The opening is 42x30mm to let the conical light beam reach the camera sensor without causing any extra vignetting. It's placed about 50 mm in front of the sensor. Two handles let me remove it easy.

I made the baffle 3 mm thick, more than needed.

Inserted in the off-axis adapter seen from telescope side.

Every time I need to clean the sensor the baffle must be removed I thought, but it's possible to clean the sensor with it installed.

Seen from camera side it looks like this. At the bottom the outlet to the guide camera and now it remind me, I must have an opening for the guide camera.

I designed another baffle with an optional hole for the off-axis guide camera's prism.

Inserted the baffle into the off-axis guider and now it's ready for next clear sky. It was possible to clean the sensor even when the mask is installed.

Here you can see that there are some stuff protruding in front of the camera sensor from the camera itself. The mirror on the left side, a hook at bottom. That can be seen on the top image of this page and this baffle can't do anything about that. To overcome that problem I have to built a new camera house or at least cut away some parts. I have already bought an another Nikon D800 camera for that coming project which will include removing IR block filter.

Second baffle:

The rectangular baffle that I placed where the prism for auto guider is helped a lot, but still there are traces of the circular pattern. Looking once again at the optical parts. This is the inlet to the 3" field flatter. There is a small area at the entrance where the arrow point that maybe can give reflections. The opening of this mammoth field flatter sounds big with its 68 mm, but at a distance of 137 mm from the sensor a 70+ mm opening had been better.

For the second baffle I used a better calculation of the baffle's opening. I calculated it in a spreadsheet, found that baffle 1 should have been 1 mm bigger. It's not precise equations behind but good enough for this purpose. I rounded the figures upwards in the 3D-CAD design.

I found the threads at the field flatter's opening must be 76x1 or 77x1 mm. Designed a baffle with threads on the outside. The rounded corners came from the conical light beam from the triple lens.

The baffle is 2.5 mm thick, behind is the inner baffle at the prism.

This is direct out from 3D-printer, some work to do before installation.

Installed and in correct angle, the rectangular opening must be in line with the sensor. The other two small circular holes only used when it's installed (screwed in).

A deeper look into off-axis adapter. Where it ends the camera's opening take over. The arrows point on stuff that could be seen in the images as shadows. Especially the mirror at right shadows a big part of the sensor when big optics is used. That's the one I will try to remove later.

With rectangular baffles it's important that camera, off-axis adapter and field flatter sit at correct angle relative each other. I have these markings to check that they hasn't rotate.

A look through the telescope's front lens.

1. baffle at guide prism
2. baffle at front of field flatter
3. focuser draw tube
4. telescope's internal baffle
5. telescope's internal baffle

I have to make a new MasterfFlat too, after that I can do a new test. My hope this baffles will remove the ghost rings or at least reduce them a lot, also the contrast in the image will be better. I must test my ideas of what cause this problem to solved it.

Light leakage:

One more thing to check, is there any light leakage through the plastic adapter? I wrapped it with aluminum foil and did some test, no indication what I could see of any light leakage.